Isn't this just the status quo on phone/tablet devices? Windows 8 is basicaly a phone/tablet OS targeted at that market. Undoubtably some of the devices will have screens and keyboards and look like desktop PCs, but will have finally abandoned the PC boot heritage. As on the mobile devices, you'll have to wait until the jailbreak becomes widely available and use that.

Don't forget that signed malware is not impossible (qv the DigiNotar CA compromise recently). It'll be entertaining once the signed malware gets in and blacklists the official Windows keys while whitelisting its own, resulting in a system where you can't remove the virus .. unless you re-jailbreak it.